Dermatitis is a general term that refers to inflammation in the skin. In dogs and cats, dermatitis may be caused by yeast or bacterial infections in the skin.
How Yeast and Bacterial Dermatitis Happens in Dogs and Cats
Skin infections caused by yeast and bacteria rarely happen alone. Under normal circumstances, both canine and feline skin provides a defensive barrier that bacteria and yeast are unable to breach. However, when your dog or cat's skin becomes damaged, the environment on the surface of the skin changes. This change gives the normal yeast and bacteria living on the surface of the skin the opportunity to avoid the skin's normal defense systems and cause further damage to the skin.
If your dog or cat has been scratching excessively or has been losing his hair, it is possible that his skin has become infected by either bacteria or yeast. Various skin diseases can cause changes in the skin that can allow yeast and bacteria to invade and infect the skin. Potential underlying causes include:
- Allergic skin diseases, such as flea allergy, food allergy or atopy
- Infectious skin disease, such as Demodectic mange
- Metabolic skin disease, such as that caused by hypothyroidism or hyperadrenocorticism in dogs
Any disease process that damages or removes the skin's natural defensive measures can be a predisposing cause of a yeast and/or bacterial skin infection.
The skin may be infected by numerous types of bacteria, including Streptococcus, Staphylococcus, E. Coli, Proteus, Pseudomonas and many others. The most common yeast infection seen in the skin is caused by Malassezia.
Symptoms of Secondary Bacterial or Yeast Infections in Dogs and Cats
Both yeast and bacterial skin infections will make your dog or cat extremely itchy. The symptoms seen will vary, depending on the underlying cause of the skin infection. However, reddened skin, hair loss, scabs and open sores are all possibilities with both yeast and bacterial skin infections.
Diagnosing Canine and Feline Bacterial and Yeast Dermatitis
The test most commonly used to diagnose bacterial and yeast dermatitis is skin cytology. Skin cytology involves collecting cells from the surface of the skin, dying them with special stains and examining the cells under a microscope.
- Both yeast and bacteria will be visible in the skin cytology samples.
- Malassezia yeast organisms are readily identified using skin cytology.
- Bacterial organisms can be classified into basic groups based on their shape and which stains they can be dyed with.
In some circumstances, a bacterial culture and sensitivity may need to be done to precisely identify the type or types of bacteria and determine which antibiotic will be effective in killing or controlling the bacteria. However, in most cases, an antibiotic selection can be made based on knowing which bacterial groups are present as determined on the skin cytology.
Treatment of Bacterial and Yeast Skin Infections in the Dog and Cat
Treatment of canine and feline skin infections caused by yeast require treatment with an anti-fungal medication. Commonly used medications include ketoconazole, itraconazole, griseofulvin and other anti-fungal medications.
Treatment of bacterial skin infections relies on antibiotics. The initial antibiotic chosen is often based on the results of the skin cytology. Commonly chosen antibiotics include cephalexin, amoxicillin/clavulanic acid, trimethoprim/sulfa and others. If the infection is not responsive to the initially chosen antibiotic, a bacterial culture and sensitivity may identify a more effective antibiotic choice.
One of the most important things to remember in treating secondary bacterial and yeast skin infections in dogs and cats is that there is almost always an underlying disease that caused the skin to be susceptible to infection. This underlying cause must be identified and treated if treatment of the skin infection is to be successful. If the underlying cause of the infection is not treated, the skin infection is likely to return.